Working device for inner wall surface of tower tank, and inner wall surface working method using the same

ABSTRACT

By using a construction in which a suspended beam structure ( 9 ) is suspended from a suspension support base ( 8 ) that has been installed inside a tower structure ( 1 ), in a manner that enables movement up and down of the suspended beam structure, an operations unit ( 20 ) is attached to the suspended beam structure ( 9 ) via a guide mechanism (Z), in a manner that enables movement up and down, and/or left and right, and operations such as welding are then performed on an inner wall surface ( 1   d ) of the tower structure ( 1 ) using the operations unit ( 20 ), the operating height position for the operations unit ( 20 ) is easily altered by moving the suspended beam structure ( 9 ) up or down, the operation for adjusting levels during operations is markedly simplified, or even unnecessary, and the safety and operating efficiency of operations is improved.

TECHNICAL FIELD

The present invention relates to an operations apparatus for performinga variety of operations on an inner wall surface of a tower structure,and an operational method that uses such an operations apparatus. Inparticular, the invention relates to an operations apparatus and anoperations method for performing welding operations on the inner wallsurface of a tall tower structure used under conditions of high pressureand high temperature.

BACKGROUND ART

Many methods have been proposed for performing the various operations onthe inner wall surface of a tower structure, including putting up ascaffold within the inside of the tower structure, but no operationsapparatus or operational method has yet appeared that could be said tobe satisfactory in terms of operating efficiency, operating time, andsafety.

Operations on the inner wall surface of a tower structure includewelding, inspections, modifications, and cleaning, and weldingoperations have been the most needful of improvements in terms ofcontinuity of the operation, danger, and the welding system.

For example, in a paper production plant, the digester, which is thepressure vessel with a blast furnace type construction that is used inpulp dissolution, is used under conditions of high temperature and highpressure, and in the type of environment that accompanies the chemicalreaction between the contents and the chemicals used, and consequently,is specified in the safety standards as a type 1 pressure vessel.

In this type of tower structure, prolonged use of the tower requiresthat inspections, cleaning, welding, and modification operations areperformed frequently. Particularly in the digester, which is apressurized vessel, prolonged use raises concerns about the developmentof secular cracking defects such as stress corrosion cracking. This typeof stress corrosion cracking develops due to the combined action of anumber of factors including deterioration factors such as localizedchanges in the material (typically steel plate) that forms the innerwall surface of the digester, stress factors such as tensile residualstress arising from the heat generated during welding, and corrosionenvironment factors resulting from either high temperatures and highpressure or from chemical reactions, and moreover the cracks graduallygrow over time. As a result, there is a danger that cracks caused bythis stress corrosion cracking may penetrate right through the wall ofthe digester, in some cases causing a major accident within the plant.Furthermore, in addition to crack type defects such as the stresscorrosion cracking described above, it is also common knowledge thatduring prolonged use of the digester, the contents (such as pulpmaterial and the like) continually grind against the inner wall surfaceof the digester under a high temperature, high pressure environment,gradually wearing away the inner walls and reducing their thickness.

Because of these circumstances, digesters must be maintained at thesafety standard for a type 1 pressure vessel, and the thickness of thewall sections must not only meet a design thickness deemed necessary toensure a strong design, but must also include an additional level ofexcess thickness to ensure a predetermined safety factor.

However, even if a predetermined level of excess thickness is added tothe thickness of the wall sections in this manner, prolonged use stillresults in the unavoidable development of crack type defects and areduction in wall thickness arising from abrasion, and accordingly, theinterior of the digester is inspected regularly for corrosion and wearand the like after a predetermined period of operation, and the requitedrepair operations are carried out where necessary. For example, in thecase of a crack type defect, possible actions include overlay repairmethods in which the defective section is removed, and overlaying isused to recover the thickness to its original value, and lining methodsin which the area incorporating the crack type defective section iscovered with a repair plate, which is then welded in place to isolatethe crack type defective section from the corrosive environment andprevent any further growth of the crack. Furthermore, for abrasion basedthinning of the walls, one possible measure is an “overlay method” inwhich overlay welding is performed within those sections of reducedthickness to recover the thickness to its original value. An “overlaymethod” is a technique that is particularly effective for repairing anyof the above problems, and is gaining attention as an ideal techniquefor prolonging the life of tower structures such as digesters.

However, in cases where this “overlay method” is employed as a methodfor countering the shortening of the life of a tower structure such as adigester resulting from thinning of the walls, the following types ofproblems arise.

Namely, in cases where repair of the wall surfaces of a tower structureis undertaken via this “overlay method”, the reduced thickness sectionsof the inner surfaces (that is, the targeted regions for repair) must beentirely covered with as uniform a cladding as possible, andconsequently operational control of factors such as the width of theweld bead and the spacing between adjacent weld beads is essential.

In such cases, and particularly in cases in which the tower structurebeing worked upon is a large scale, very high structure such as adigester, entrusting this operational control entirely to the actionsand judgment of an operator has limits in terms of ensuring an adequatelevel of control precision and achieving an effective extension of thelife of the digester through overlay welding, and some form of automatedtechnique is required.

Accordingly, an object of the present invention is to provide anoperations apparatus for the inner wall surface of a tower structurethat enables various operations performed on the inner wall surface ofthe tower structure to be conducted in a safer operating environment,with good operability and good reliability, as well as an operationalmethod that utilizes such an operations apparatus.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, in a first aspect of the presentinvention, a suspension support base is installed inside a towerstructure, a suspended beam structure is suspended from the suspensionsupport base in a manner that enables movement up and down, a weldingunit is attached to the suspended beam structure via a guide mechanismin a manner that enables movement up and down, and/or left and right,and operations are performed on the inner wall surface of the towerstructure using the operations unit.

According to an operations apparatus for the inner wall surface of atower structure according to the first aspect of the present inventiondescribed above, by moving the suspended beam structure suspended belowthe suspension support base in an upward or downward direction, theheight position within the tower structure of the operations unitattached to the suspended beam structure, in other words, the heightsetting within the tower structure for the operational target region forthe operations unit, can be easily altered, and compared with aconventional case where a scaffold is put up inside the tower structure,and the height of the scaffold has to be changed every time theoperating height is altered, the operation for adjusting levels duringoperations is markedly easier, or even unnecessary, which provides anequivalent improvement in the safety and operability associated with allmanner of operations.

In addition, because the operations unit is attached to the suspendedbeam structure via the aforementioned guide mechanism, allowing theoperations unit to be moved up and down, and/or left and right, controlof the required operations performed using the operations unit (forexample in the case of welding operations, control of the width of theweld bead, the weld direction, or the spacing between adjacent weldbeads) is far easier and more reliable than the case in which thiscontrol depends solely upon the actions and judgment of the operator,and as a result, a very uniform operation will be conducted over anentire required height region with excellent reliability, therebyensuring an effective extension of the life of the tower structure.

Furthermore, a second aspect of the present invention is the operationsapparatus for the inner wall surface of a tower structure describedabove, wherein the aforementioned guide mechanism comprises an upperguide structure and a lower guide structure that are separated andoppose each other across the vertical direction, and a vertical guidestructure, which extends between each of the guide structures and isdisposed in the vertical direction, is able to move in a left and rightdirection along the upper and lower guide structures, and supports theaforementioned operations unit in a manner that enables up and downmovement.

According to an operations apparatus for the inner wall surface of atower structure according to the second aspect of the present invention,which has the type of structure described above, because the guidemechanism is a simple and low cost mechanism formed from the upper guidestructure, the lower guide structure and the vertical guide structure,an inner wall surface operations apparatus that displays the effects ofthe first aspect of the present invention will be provided at lowercost, and this contributes to a reduction in operating costs.

In addition, a third aspect of the present invention is the operationsapparatus for the inner wall surface of a tower structure describedabove, wherein the aforementioned operations unit is equipped with atleast welding, inspection, modification, and cleaning functions.

According to an operations apparatus for the inner wall surface of atower structure according to the third aspect of the present invention,the following characteristic effects will be achieved in addition to theeffects provided by the first or second aspects of the invention.Namely, in this aspect of the invention, because the operations unit isequipped with at least welding, inspection, modification, and cleaningfunctions, these various operations on the inner wall surface of thetower structure can be performed conjointly, and all of the operationswill be performed highly efficiently with a high level of reliability.

In addition, a fourth aspect of the present invention is the operationsapparatus for the inner wall surface of a tower structure describedabove, wherein a post is set up in a vertical direction inside the towerstructure, and a height adjustable operations platform is installed thatcan be raised and lowered under its own power in the vertical directionalong this post.

According to an operations apparatus for the inner wall surface of atower structure according to the fourth aspect of the present invention,the following characteristic effects will be achieved in addition to theaforementioned effects provided by the first, second or third aspect ofthe invention. Namely, in this aspect of the invention, because a postis set up in the vertical direction inside the tower structure, and aheight adjustable operations platform is installed that can be raisedand lowered under its own power in the vertical direction along thispost, by raising and lowering the height adjustable operations platformunder its own power in the vertical direction along the post, the heightadjustable operations platform can be used to move operating materialsor operators safely and rapidly to the operating position for theoperations unit, without requiring any scaffold height adjustments, evenif the tower structure is a blast furnace type structure of considerableheight. As a result, both operational speed and safety are achieved,which leads to a reduction in the overall operational costs associatedwith the inner wall surface operations apparatus.

Furthermore, a fifth aspect of the present invention is the operationsapparatus for the inner wall surface of a tower structure describedabove, wherein a fixed operations platform is attached to the post, thefixed vertical position of the fixed operations platform relative to thepost can be set and altered, and alteration of the fixed position of thefixed operations platform is performed by raising or lowering the heightadjustable operations platform.

According to an operations apparatus for the inner wall surface of atower structure according to the fifth aspect of the present invention,which has the type of structure described above, the followingcharacteristic effects will be achieved in addition to theaforementioned effects provided by the fourth aspect of the invention.Namely, in this aspect of the invention, because the fixed verticalposition, relative to the post, of the fixed operations platformattached to the post can be set and altered, by fixing the fixedoperations platform at a height position corresponding with theoperating position for the operations unit, an operator rides on thefixed operations platform, and easily and accurately conducts qualitycontrol of the operations performed by the operations unit, enablingoperations to be conducted with even greater reliability.

In addition, because positional alteration of the fixed operationsplatform is performed by raising or lowering the height adjustableoperations platform, the operation for altering the position of thefixed operations platform would be performed safely and rapidly, withoutrequiring any related operations such as scaffold height adjustments andthe like, enabling good operational safety and a reduction in operatingcosts.

Furthermore, an operational method for an inner wall surface accordingto a sixth aspect of the present invention comprises the steps ofinstalling a suspension support base inside a tower structure,suspending a suspended beam structure from the suspension support basein a manner that enables movement up and down, attaching an operationsunit to the suspended beam structure via a guide mechanism in a mannerthat enables movement up and down, and/or left and right, and performingoperations on the inner wall surface of the tower structure using theoperations unit.

According to the type of operational method for an inner wall surfaceaccording to the sixth aspect of the present invention, a suspensionsupport base is installed inside a tower structure, a suspended beamstructure is suspended from the suspension support base in a manner thatenables movement up and down, an operations unit is attached to thesuspended beam structure via a guide mechanism in a manner that enablesmovement up and down, and/or left and right, and operations areperformed on the inner wall surface of the tower structure using theoperations unit, and consequently, by moving the suspended beamstructure suspended below the suspension support base in an upward ordownward direction, the height position within the tower structure ofthe operations unit attached to the suspended beam structure, in otherwords, the height setting within the tower structure for the operationaltarget region for the operations unit, would be easily altered, andcompared with a conventional case where a scaffold is erected inside thetower structure, and the height of the scaffold has to be changed everytime the operating height is altered, the operation for adjusting levelsduring operations is markedly easier, or even unnecessary, and thisenables an improvement in the safety and operability associated with allmanner of operations.

In addition, because the operations unit is able to move up and down,and/or left and right, control of the operating status of operationsperformed using the operations unit is extremely simple and reliable,and a very uniform operation will be conducted over an entire requiredheight region with excellent reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the operational state when anoperations apparatus according to the present invention is used toperform an overlay welding operation on the inner wall surface of adigester.

FIG. 2 is an enlarged view along the arrow headed line II-II of FIG. 1.

FIG. 3 is an enlarged exploded perspective view showing the structure ofthe section III shown in FIG. 2.

FIG. 4 is an enlarged view along the arrow headed line IV-IV of FIG. 1.

FIG. 5 is an enlarged view along the arrow headed line V-V of FIG. 1.

FIG. 6 is an enlarged view along the arrow headed line VI-VI of FIG. 1.

FIG. 7 is an enlarged view along the arrow headed line VII-VII of FIG.1.

FIG. 8 is an enlarged view of the section VIII shown in FIG. 1.

FIG. 9 is an enlarged view along the arrow headed line IX-IX of FIG. 8.

FIG. 10 is a view along the arrow headed line X-X of FIG. 9.

FIG. 11 is an enlarged view along the arrow headed line XI-XI of FIG. 1.

FIG. 12 is a view along the arrow headed line XII-XII of FIG. 11.

FIG. 13 is a diagram describing the state of weld beads.

FIG. 14 is a cross-sectional view along XIV-XIV of FIG. 13.

BEST MODE FOR CARRYING OUT THE INVENTION

As follows is a description of an operations apparatus and anoperational method according to the present invention, with reference tothe drawings and using an apparatus for a welding operation, and theoperational method therefor, as a representative example.

FIG. 1 shows a digester 1 (tower structure), which is the pressurevessel of a blast furnace structure used in a paper production plant,with an overlay welding operations apparatus (inner wall surfaceoperations apparatus) for conducting overlay welding on required areasof the inner wall surface of the digester 1 disposed therein.

A: Configuration of the Digester 1

The digester 1 is, for example, a large scale, tall, closed vessel withan internal diameter of 4 to 5 meters and a height of 40 to 50 meters,and is classified as a type 1 pressure vessel in the safety standards.Accordingly, the thickness of the walls must be maintained above adefined constant thickness, and if the wall thickness is exposed tohigher than expected abrasion, then in order to extend the life of thestructure, a repair operation must be conducted to return the thicknessto its original value, as described above. In this embodiment, an“overlay method” is adopted as the method of repairing the wall surfacesof the digester 1, which involves extra thickness being attached to theinner wall surface using overlay welding, and the overlay weldingoperations apparatus described above is used for executing this overlaywelding.

The aforementioned digester 1 is formed as a sealed vessel, comprising amain body section 2 with a large diameter cylindrical structure, with adigester bottom structure 3 joined at one end and a digester topstructure 4 joined at the other end, and is fixed in a vertical positionwith a bottom section 1 a of the digester bottom structure 3 supportedon a base 5. The main body section 2 is constructed so that the diameterdimension reduces in a stepwise manner from the bottom section 1 a ofthe digester 1 through to a top section 1 b, and a device such as astrainer (not shown in the drawing) is disposed in those regions wherethe diameter dimension reduces.

Furthermore in this embodiment, when overlay welding is performed on theinner wall surface of the digester 1 using the aforementioned overlaywelding operations apparatus, in order to ensure good ventilationthrough the digester 1, manholes that are provided in the digester 1 forthat purpose are used. In other words, an exhaust system 32 is attachedto a bottom manhole 31 provided in a central position within thedigester bottom structure 3, a large diameter manhole 35 providedsubstantially halfway up the digester is used as a natural air inlet,and additional exhaust systems 33, 34 are disposed at a pair of upperand lower manholes provided toward the top section 1 b. During overlaywelding operations, by supplying external air naturally through themanhole 35 to the inside of the digester 1, and then exhausting the airfrom each of the exhaust systems 32, 33, 34, air circulation isestablished within the digester 1, ensuring a good working environmentinside the digester 1, and thereby guaranteeing a highly safe operation.

In addition, during overlay welding operations, a manhole 36 providednear the bottom section 1 a of the digester 1 is used for introducingmaterials or allowing people to enter or exit from the digester 1, whilea suspension support base 8, which is described below, is attached usingfour scaffold nozzles 26, 26, . . . (see FIG. 5) provided directly belowthe manhole equipped with the exhaust system 34.

In this embodiment, the execution of overlay welding using the overlaywelding operations apparatus is described below for those sections ofthe inner wall surface of the digester 1 that are positioned below theattachment position of the suspension support base 8. Needless to say,by positioning the suspension support base 8 toward the top section 1 bof the digester 1, overlay welding is performed along the entire heightof the main body section 2.

B: Configuration of the Overlay Welding Operations Apparatus

As shown in FIG. 1, the aforementioned overlay welding operationsapparatus comprises a left and right pair of posts 16, 16 (describedbelow) disposed in a parallel upright manner with a predeterminedspacing therebetween, which extend between a lower fixed operationsfloor 6 (described below) that is disposed near the bottom section 1 aof the digester 1, and an upper fixed operations floor 7 (describedbelow) that is disposed toward the top section 1 b, and a heightadjustable operations platform 14 (described below) that can be raisedand lowered under its own power, and a fixed operations platform 13(described below) are attached to each of the posts 16, 16, a suspendedbeam structure 9 (described below) is suspended from the aforementionedsuspension support base 8 (described below) in a manner that enablesmovement up and down, and a plurality of welding units 20 (whichcorrespond with the “operations unit” disclosed in the claims) areattached to the suspended beam structure 9 via a guide mechanism Z(described below) in a manner that enables free movement up and down,and/or left and right (in a circumferential direction) of each weldingunit. As follows is a separate description of each of the structuralelements of this overlay welding operations apparatus.

(B-1) Posts 16

As shown in FIG. 1 and FIG. 8, the posts 16 are formed from trussstructured post pieces 16 a, 16 a, . . . with a rectangularcross-section and a predetermined axial length, a predetermined numberof which are joined together sequentially in an axial direction to forma column type structure. The posts 16, 16 are integrated together intoan approximately ladder type structure by joint members 17, 17, . . .that are attached to the posts at predetermined intervals along theaxial direction, and by fixing the bottom end of the ladder structure tothe lower fixed operations floor 6 that is described below (see FIG. 2)and fixing the top end to the upper fixed operations floor 7 that isdescribed below (see FIG. 4), the posts 16, 16 are secured in a verticaldirection inside the digester 1.

In this embodiment, the aforementioned posts 16 utilized two parallelcolumns separated by a predetermined spacing, and as described below, aguiding action and a support function for the fixed operations platform13 and the height adjustable operations platform 14 is achieved throughinteraction with these two posts 16, 16, but the actual number of posts16 installed in the present invention can be suitably increased ordecreased as required, and in other embodiments, either a single post,or three or more parallel posts can be provided.

The operational procedure used to set up a post 16 using theaforementioned post pieces 16 a, 16 a, . . . is as follows. Namely,first the bottommost pair of posts 16, 16 are secured in an uprightorientation at predetermined positions on top of the aforementionedlower fixed operations floor 6. Subsequently, the height adjustableoperations platform 14 that is described below is assembled tocorrespond with each of these bottommost posts 16, 16, and is producedso as to be able to be raised and lowered under its own power. Anoperator and the aforementioned post pieces 16 a, 16 a, . . . forjoining to the posts are then loaded onto this height adjustableoperations platform 14, and with the height adjustable operationsplatform 14 being raised and lowered along the already secured posts 16,16, the operation of joining new posts 16 to the top end of the existingposts 16 is repeated until the aforementioned upper fixed operationsfloor 7 is reached. In other words, in this embodiment, the operation ofsetting up the posts 16 does not require the conventional type ofprefabricated steel scaffold, and consequently, the operationsassociated with altering the height of the scaffold are unnecessary,which enables the operation of setting up the posts 16 to be completedsafely and quickly.

A rack 15 that functions as one portion of the height adjustmentmechanism of the height adjustable operations platform 14 is provided onone side of each the posts 16, 16, and runs along the lengthwisedirection of each post 16, 16.

Furthermore, because the aforementioned post pieces 16 a are carriedinto the digester 1 through the manhole 36, the post pieces must be setto a size and shape that enables passage through the manhole 36.

(B-2) Lower Fixed Operations Floor 6

As shown in FIG. 1, the lower fixed operations floor 6 described aboveis secured in an intermediate position between the position immediatelyabove the digester bottom structure 3 of the digester 1, and theposition immediately below the manhole 36, and is used as an “operationsplatform” as per its original function, but also performs the importantfunction of acting as a support base for the posts 16, 16.

In other words, as shown in FIG. 2, the lower fixed operations floor 6is constructed by attaching four support girders 43, 43, . . . in across girder arrangement, and then installing and fixing a flooringmaterial 44 in a circular shape, the periphery of which extends out to aposition close to, and facing the inner wall surface id of the side wall1 c, on top of these support girders 43, 43, . . . . Then, the posts 16,16 are secured by mounting the bottom ends of the posts 16, 16 (that is,the bottom end of the post piece 16 a positioned at the bottommost endof each post 16) onto a left and right pair of support bases 41, 41provided toward the center of the lower fixed operations floor 6,restricting the movement of the posts via positioning stoppers 42, 42, .. . positioned at the outer periphery of the posts, and bolting theposts to the support bases via securing bolts (not shown in thedrawing).

The most characteristic feature of the lower fixed operations floor 6 isthe construction used to secure each of the support girders 43, 43, . .. to the digester 1. Namely, in this embodiment, as shown in FIG. 2 andFIG. 3, protruding securing pieces 45 are welded to the inner wallsurface 1 d of the side wall 1 c at a position directly above theaforementioned digester bottom structure 3 of the digester 1, and eachsecuring piece 45 and the end of a support girder 43 are securedtogether in a detachable manner via a connecting member 46. Thesesecuring pieces 45 are fixed around the periphery of the inner wallsurface 1 d with a predetermined spacing, so as to be positioned at eachend of each of the four support girders 43, 43, . . . respectively.Then, when the overlay welding operations have been completed and thelower fixed operations floor 6 has been disassembled and removed, thesesecuring pieces 45, 45, . . . remain attached to the digester 1, and thepulp digestion operation using the digester 1 is conducted with thesesecuring pieces 45 still secured in place.

In this manner, the lower fixed operations floor 6 is attached to thebottom section 1 a of the digester 1 via the securing pieces 45, 45, . .. , and by securing and supporting the posts 16, 16 on this lower fixedoperations floor 6, the dead load of the posts 16, 16, the dead load ofthe fixed operations platform 13 and the height adjustable operationsplatform 14 described below, which are attached to the posts 16, 16, andthe weight of the materials loaded onto each of these operationsplatforms 13, 14 are all transferred from the lower fixed operationsfloor 6, through the securing pieces 45, 45, . . . and onto the sidewalls 1 c of the digester 1, where they are safely supported. As aresult, absolutely no load from the posts 16, 16 is applied to theaforementioned digester bottom structure 3 positioned below the lowerfixed operations floor 6, and any damage or the like to the digesterbottom structure 3 will be effectively prevented. This effect isparticularly important considering that the shape of the digester bottomstructure 3 means that the production costs are higher than those of thecylindrically shaped main body section 2.

The aforementioned lower fixed operations floor 6 is the first structureset up when overlay welding operations are to be undertaken, andsubsequent operations such as the transporting of various materials, andthe assembling of the aforementioned posts 16, 16 or the heightadjustable operations platform 14 are performed using this erected lowerfixed operations floor 6 (in other words, it performs its primaryfunction as an operations platform). Furthermore, because the lowerfixed operations floor 6 is carried into and out of the digester 1through the aforementioned manhole 36, each of the structural elementsmust be able to be disassembled down to a size capable of passingthrough the manhole 36 (not shown in the drawings).

(B-3) Upper Fixed Operations Floor 7

The upper fixed operations floor 7 described above is disposed at aposition immediately below the digester top structure 4 of the digester1 (see FIG. 1), has a circular, flat shape, and is positioned inside theside walls 1 c of the digester 1 with a predetermined space retainedbetween the floor and the side walls 1 c. This upper fixed operationsfloor 7 is connected and secured to the top ends of the posts 16, 16 viaa left and right pair of post securing members 50, 50 that are providedtoward the center of the floor, while movement in the horizontaldirection is regulated by bracing the tips of jacks 51, 51, . . .provided at four locations around the outer periphery of the flooragainst the inner wall surface id of the side walls 1 c.

Because this upper fixed operations floor 7 is carried into and out ofthe digester 1 through the aforementioned manhole 36, each of thestructural elements must be able to be disassembled down to a sizecapable of passing through the manhole 36 (not shown in the drawings).

(B-4) Suspension Support Base 8

The suspension support base 8 described above is disposed horizontallyat a position toward the top section 1 b of the digester 1, and supportsthe suspended guide mechanism Z described below, and as shown in FIG. 5and FIG. 8, is constructed by inserting and engaging a girder member 55,via bearings 57, through a pair of scaffold nozzles 26, 26 formed in theside walls 1 c of the digester 1 in opposing positions along anidentical axis sitting to one side of the centerline of the digester,and through another pair of scaffold nozzles 26, 26 formed in opposingpositions along an identical axis sitting to the other side of thecenterline respectively, and then connecting this pair of girder members55, 55 with joining members 56. The aforementioned posts 16, 16 passvertically through the central section of this suspension support base8, which is disposed horizontally across the inside of the digester 1.

Furthermore, suspension positions P₁, P₁, . . . are set at fourpositions near the connection points between each of the girder members55, 55 and each of the joining members 56, 56 of the suspension supportbase 8. Then, as shown in FIG. 8, a chain block 18 is attached at eachof these suspension positions P₁, P₁, . . . .

Because this suspension support base 8 is carried into and out of thedigester 1 through the aforementioned manhole 36, each of the structuralelements must be able to be disassembled down to a size capable ofpassing through the manhole 36 (not shown in the drawings).

(B-5) Suspended Beam Structure 9

The suspended beam structure 9 described above is suspended from andsupported by the aforementioned suspension support base 8, via each ofthe aforementioned chain blocks 18, 18, . . . , and supports thesuspended guide mechanism Z described below, and as shown in FIG. 6 andFIG. 8, is constructed by attaching to the top of a pair of girdermembers 58, 58 disposed in parallel with a predetermined spacingtherebetween, a pair of girder members 59, 59 that sit orthogonallyrelative to the girder members 58, 58, thereby forming a cross girderarrangement, and then attaching a pair of girder members 61, 61 thatextend between the end sections at both ends of the pair of girdermembers 59, 59, and attaching pairs of girder members 60, 60 that extendfrom the girder member 58 across the corresponding girder member 61 in aradial direction.

Then, in this suspended beam structure 9, suspension positions P₂, P₂, .. . , each of which corresponds with one of the suspension positions P₁,P₁, . . . on the suspension support base 8, are set on top of theaforementioned pairs of girder members 59, 59, and the chains 19, 19, .. . hanging down from each of the chain blocks 18 positioned at thesuspension support base 8 are connected to each of these suspensionpositions P₂, P₂, . . . , so that the suspended beam structure 9 issuspended from, and supported by the suspension support base 8 via thesechains 19, 19, . . . , and can be raised or lowered vertically bywinding each of the chains 19, 19, . . . in, or back out.

Furthermore, suspension positions P₃, P₃, . . . are set on the girdermembers 59, 59 containing the aforementioned suspension positions P₂ andon each of the girder members 60, 60, so as to be positioned on anidentical circumference, with an identical pitch around thecircumferential direction. Chain blocks 27, 27 are attached to each ofthese suspension positions P₃, P₃, . . . and a wire supply device 21 ofa welding unit 20 described below is suspended via a chain 28 hangingdown from each chain block 27, 27, . . . .

In addition, the end sections of the aforementioned pair of girdermembers 58, 58 of the suspended beam structure 9, and the end sectionsof each of the girder members 60, 60 are positioned on an identicalcircumference, with a predetermined pitch around the circumferentialdirection. These end sections function as the suspension and supportpoints for the guide mechanism Z described below, and a suspension link29 is attached to each end section.

Because this suspended beam structure 9 is carried into and out of thedigester 1 through the aforementioned manhole 36, each of the structuralelements must be able to be disassembled down to a size capable ofpassing through the manhole 36 (not shown in the drawings).

(B-6) Guide Mechanism Z

The guide mechanism Z described above guides the movement of the weldingunits 20 described below, enabling good overlay welding to be conductedby the welding units 20, and comprises an upper guide structure 10, alower guide structure 11, and a vertical guide structure 12, each ofwhich is described below.

(B-6-1) Upper Guide Structure 10

As shown in FIG. 6, and FIG. 8 through FIG. 10, the aforementioned upperguide structure 10 is constructed from an annular body (see FIG. 6)formed by curved molding of H-shaped steel (see FIG. 9), with the pairof flanges in a vertical arrangement, to enable the body to bepositioned inside the inner wall surface 1 d of the digester 1. Thisupper guide structure 10 is suspended from the suspended beam structure9 via the aforementioned suspension links 29, 29, . . . , moves up anddown in concert with the raising and lowering of the suspended beamstructure 9, and as shown in FIG. 9, is supported against the inner wallsurface id by bracing the tips of jacks 63, 63, . . . that are attachedto each of the suspension links 29, 29, . . . against the inner wallsurface 1 d of the digester 1.

Furthermore, the upper guide structure 10 guides the movements of thevertical guide structure 12 described below in the left and rightdirections (that is, the circumferential direction of the inner wallsurface 1 d), and of the pair of flanges, the flange that is positionedon the inside in a radial direction is designed to function as a guiderail for the vertical guide structure 12, and consequently a saddle 37for the vertical guide structure 12 is latched onto this inside flange(see FIG. 9 and FIG. 10).

Because the upper guide structure 10 is carried into and out of thedigester 1 through the aforementioned manhole 36, each of the structuralelements must be able to be disassembled down to a size capable ofpassing through the manhole 36 (not shown in the drawings).

(B-6-2) Lower Guide Structure 11

As shown in FIG. 6, and FIG. 8 through FIG. 10, the lower guidestructure 11 described above is constructed from an annular body (seeFIG. 6) formed by curved molding of L-shaped steel (see FIG. 9), withone of the flanges directed along the radial direction and the otherflange directed upward, to enable the body to be positioned inside theinner wall surface 1 d of the digester 1. This lower guide structure 11is supported by the upper guide structure 10 via the vertical guidestructure 12 that is described below, moves up and down when the upperguide structure 10 moves up and down in concert with the raising andlowering of the suspended beam structure 9, and as shown in FIG. 9, issupported against the inner wall surface 1 d by bracing the tips ofjacks 64, which are disposed with a predetermined spacing around theperiphery of the lower guide structure 11, against the inner wallsurface 1 d of the digester 1.

As shown in FIG. 9 and FIG. 10, the connection between theaforementioned lower guide structure 11 and the vertical guide structure12 described below is achieved by sandwiching one flange section of thelower guide structure 11 between a fixed bracket 71, which is supportedby a check bolt 72 that is inserted through a slotted hole 74 formed ina vertical direction in the bottom end section of the vertical guidestructure 12, and a push bolt 73 that is attached to the vertical guidestructure 12. Furthermore, by loosening the push bolt 73, loosening thecheck bolt 72 and moving the fixed bracket 71 upward, the connectionbetween the lower guide structure 11 and the vertical guide structure 12are released.

(B-6-3) Vertical Guide Structure 12

As shown in FIG. 9 and FIG. 10, the vertical guide structure 12 isconstructed from a batten plate structure of a predetermined length, oneend (the top end) of which is attached to the saddle 37 described below.The vertical guide structure 12 guides the up and down movements of thewelding units 20 described below, and by moving the vertical guidestructure 12 in the left and right directions under the guidance of theupper guide structure 10 and the lower guide structure 11, the weldingunits 20 are also movable in the left and right direction.

The saddle 37 supports and suspends the vertical guide structure 12 fromthe upper guide structure 10, and enables the vertical guide structure12 to be moved in the left and right directions along the upper guidestructure 10, and as shown in FIG. 9 and FIG. 10, comprises a front andrear pair of slotted wheels 38, 38 that run along the top of the flangeof the upper guide structure 10, and a front and rear pair of unslottedwheels 39, 39. In addition, the saddle 37 is also provided with a frontand rear pair of check bolts 53, 53, which regulate the relativemovement between the saddle 37 and the upper guide structure 10 by beingscrewed in until the tips of the bolts contact the upper guide structure10, and a front and rear pair of lift prevention structures 54, 54,which are disposed so as to enable engagement against the bottom surfaceof the flange of the upper guide structure 10, and prevent the saddle 37from lifting. The aforementioned vertical guide structure 12 is thensecured so as to hang down from the saddle 37.

Furthermore, the aforementioned check bolt 72 and the push bolt 73 areprovided at the bottom end of the vertical guide structure 12, and byoperating this check bolt 72 and push bolt 73, the bottom end section ofthe vertical guide structure 12 is connectable to, and releasable from,the lower guide structure 11, as described above.

On the other hand, stoppers 40, 40 are provided at two verticalpositions on the vertical guide structure 12, and a rack 80 is attachedthat extends between these two stoppers 40, 40. Then, a welding unit 20that is described below is attached to the vertical guide structure 12,and can be raised and lowered along this rack 80.

A plurality of vertical guide structures 12 constructed in the mannerdescribed above are disposed at predetermined intervals around thecircumference of the upper guide structure 10. In this embodiment,vertical guide structures 12 are disposed at eight positions, as shownby position a through position h in FIG. 6.

(B-7) Welding Unit 20

As shown in FIG. 9 and FIG. 10, the welding unit 20 described abovecomprises a carriage 79 that straddles the vertical guide structure 12and is driven up and down along the rack 80 by the driving force from amotor 86, on which is mounted a welder main body 81, an oscillatingdevice 82, a profiling device 83, a pair of welding torches 85, 85, anda profile detector 87. Furthermore, the welder main body 81 is a devicethat automatically performs arc shielded welding in a carbon dioxide gasatmosphere (“MAG welding”), and the two welding torches 85, 85 areconnected in parallel to the welder main body 81 with a predeterminedspacing therebetween. In this embodiment, as described above, eight setsof vertical guide structures 12 are provided, and two welding torches85, 85 are mounted onto each of these vertical guide structures 12, andconsequently overlay welding is performed with a total of 16 weldingtorches 85 being used concurrently.

Each of the welding units 20 is also equipped with the aforementionedwire supply device 21 that supplies wire to the two welding torches 85belonging to that particular unit, and as described above, this wiresupply device 21 is suspended from the suspended beam structure 9 viathe aforementioned chain block 27 in a manner that enables the supplydevice to be raised and lowered. Furthermore, a hose 57 (see FIG. 8) forsupplying the shield gas to the welding torches 85 is also connected tothe welding torches 85 via the wire supply device 21.

As follows is a simple description of a method for conducting overlaywelding on the inner wall surface 1 d of the digester 1 using thewelding units 20.

In this embodiment, the aforementioned welding units 20 are used toperform overlay welding on the inner wall surface 1 d of the digester 1by “vertical downward welding,” and the state of the weld beads in thistype of overlay welding is shown in FIG. 13. In other words in thisembodiment, using the aforementioned pair of welding torches 85, 85 thatare arranged in parallel with a predetermined spacing therebetween,overlay welding is conducted by “vertical downward welding,” andconsequently as shown by the solid lines in FIG. 13, weld beads B₁, B₁from each of the welding torches 85, 85 are formed with a spacing thatcorresponds with the spacing between the welding torches. Then, afterthe welding units 20 have been moved from top to bottom, the arc isstopped temporarily. The welding units 20 are then raised once again,moved either left or right by an amount corresponding with the spacebetween the welding torches 85, 85 (in other words, the aforementionedvertical guide structure 12 is moved left or right), and the nextwelding run is conducted in a downward direction, with the weld beadsB₂, B₂ of this next run positioned between the weld beads B₁, B₁, fromthe previous run.

In this manner, by conducting the overlay welding sequentially with apredetermined pitch, an increase in the excess thickness of the sidewalls 1 c of the digester 1 (see the dimension “h” in FIG. 14) isachieved for the overlaid sections. From FIG. 14 it is evident that thedegree of weld penetration into the base metal (the inner wall surface 1d) during overlay welding is extremely small, and accordingly theheating effect on the base metal is also extremely limited, which meansoverlay welding provides an ideal method for increasing the wallthickness, although a large reason for this result is the fact that“downward welding” was used for the welding.

(B-8) Fixed Operations Platform 13

The fixed operations platform 13 described above is disposed in thevicinity of the guide mechanism Z (see the chain line in FIG. 8) and isused by an operator to control the state of the welding, and as shown inFIG. 7, is constructed by attaching a flooring material 69 to the top ofa lattice of cleats 67, 68, thereby forming a circular shaped flatstructure that follows the side wall 1 c of the digester 1. A left andright pair of post retaining members 66, 66 are provided toward thecenter of the fixed operations platform 13, and the posts 16, 16 arepositioned so as to pass through each of these post retaining members66, 66. This fixed operations platform 13 is movable in up and downdirection along the posts 16, 16, and can be secured to, and supportedby, the posts 16, 16 at any arbitrary height by selectively mountingsecuring pins (not shown in the drawing) between the post retainingmembers 66, 66 and the corresponding posts 16, 16. During the operationfor altering the installation height of this fixed operations platform13, the height adjustable operations platform 14 described next is used.

Because the fixed operations platform 13 is carried into and out of thedigester 1 through the aforementioned manhole 36, each of the structuralelements must be able to be disassembled down to a size capable ofpassing through the manhole 36 (not shown in the drawings).

(B-9) Height Adjustable Operations Platform 14

The height adjustable operations platform 14 described above is used fornormal inspections, as well as for transporting materials to the fixedoperations platform 13 or moving operators during the operations forconducting overlay welding on the inner wall surface 1 d of the digester1 with the aforementioned welding units 20, and as shown in FIG. 1 andFIG. 11, is formed as a circular shaped flat structure by attaching aflooring material 49 to the top of girder members 47, 48 that areassembled in a cross girder arrangement, with a predetermined spacingmaintained between the periphery of the platform and the inner wallsurface 1 d of the digester 1.

This height adjustable operations platform 14 is equipped with a leftand right pair of post guides 62, 62 provided in the central region ofthe platform, and the aforementioned posts 16, 16 pass through each ofthese post guides 62, 62. Travel drive motors 30, 30 are attached to oneside of each of the post guides 62, 62, namely, on the side of the posts16 to which the racks 15 are attached, and the pinion gears (not shownin the drawings) provided on the motors 30 engage with, and travel alongthe racks 15 on the side of the posts 16, enabling the height adjustableoperations platform 14 to move up and down along the posts 16, 16 underits own power.

In addition, guide wheel units 25 are provided at four locations aroundthe circumferential direction of the outer periphery of the heightadjustable operations platform 14. These guide wheel units 25 run alongthe inner wall surface 1 d of the digester 1 when the height adjustableoperations platform 14 is raised or lowered, restricting sidewaysdeviation of the height adjustable operations platform 14 and ensuringstable movement up and down. In other words, as shown in FIG. 12, theguide wheel units 25 are constructed by attaching a wheel 76 to the tipof a pivoted arm 77, which is provided on the height adjustableoperations platform 14 and is free to swing in the radial direction ofthe digester 1, and then using a damper 78 to energize the arm 77 toapply pressure continually in the outward direction. According to such aconstruction, because the wheels 76 run along the inner wall surface 1 dwhile being pressed against the inner wall surface with a constant,predetermined pressure, stability during the raising and lowering of theheight adjustable operations platform 14 is ensured at all times, andbecause the wheels 76 are free to deviate along the radial direction ofthe digester 1, the wheels 76 accommodate steps in the inner wallsurface 1 d, and easily ride over such steps, meaning the reliability ofthe movement of the height adjustable operations platform 14 is ensured.

Because the height adjustable operations platform 14 is carried into andout of the digester 1 through the aforementioned manhole 36, each of thestructural elements must be able to be disassembled down to a sizecapable of passing through the manhole 36 (not shown in the drawings).

C: Description of Operation of the Overlay Welding Operations Apparatus

As follows is a description of one example of the operating procedurefor the operation of conducting overlay welding on the inner wallsurface 1 d of the aforementioned digester 1 using the aforementionedoverlay welding operations apparatus.

For a welding operation, first, preparatory operations such as theassembling of operations platforms are carried out. In other words,first, the required materials are carried through the manhole 36provided near the bottom section of the digester 1. Then, first thelower fixed operations floor 6 is assembled at the bottom section 1 a ofthe digester 1, and the height adjustable operations platform 14 is thenassembled on top of this lower fixed operations floor 6.

Next, the height adjustable operations platform 14 is moved up and down,while the aforementioned post pieces 16 a, 16 a, . . . are joinedtogether sequentially in a stacked arrangement on top of the lower fixedoperations floor 6, forming the posts 16, 16, and then the upper fixedoperations floor 7 that is erected at the top section 1 b of thedigester 1 is secured to the top ends of the posts 16, 16. Thiscompletes the installation of the posts 16, 16.

Subsequently, assembling of the welding related equipment is conductedusing the height adjustable operations platform 14, which moves up anddown along the posts 16, 16. In other words, first the aforementionedsuspension support base 8 is assembled and secured to the digester 1,and then the suspended beam structure 9 is assembled and suspended fromthe suspension support base 8 via the aforementioned chain blocks 18. Inaddition, the upper guide structure 10 is suspended from the suspendedbeam structure 9, each of the vertical guide structures 12, 12, . . . isattached to the upper guide structure 10, and the lower guide structure11 is supported at the bottom end of each of these vertical guidestructures 12, 12, . . . . In this state, both the upper guide structure10 and the lower guide structure 11 are not secured to the inner wallsurface 1 d of the digester 1, and are movable freely in up and downdirection.

The aforementioned fixed operations platform 13 is then assembled,mounted onto the height adjustable operations platform 14, raised to apredetermined height position by raising or lowering the heightadjustable operations platform 14, and then secured to the posts 16, 16.

Meanwhile, cables 24 extending from a welding base unit 22 disposedoutside the digester 1 are passed into the digester 1 through the bottommanhole 31 of the digester 1, and are fed through to the fixedoperations platform 13, and of these cables 24, the power supply cableis connected to a welding controller 23 mounted on top of the fixedoperations platform 13, and the carbon dioxide gas supply hose isconnected to the welding units 20, 20, . . . attached to each of thevertical guide structures 12, 12, . . . .

This completes the preparatory operations required prior to the weldingoperations.

Subsequently, overlay welding using each of the welding units 20, 20, .. . is conducted on the inner wall surface 1 d of the digester 1.

First, each of the chain blocks 18, 18, . . . are moved insynchronization with each other, and the suspended beam structure 9 ismoved to a position immediately above the area targeted for welding. Atthis position, the upper guide structure 10 and the lower guidestructure 11 are then secured to the inner wall surface 1 d of thedigester 1. In addition, with each of the vertical guide structures 12,12, . . . in a state that enables relative movement with respect to theupper guide structure 10 and the lower guide structure 11 (in otherwords, a state in which both the check bolt 53 on the saddle 37, and thepush bolt 73 on the vertical guide structure 12 are loosened), theposition of each of the vertical guide structures 12, 12, . . . relativeto the inner wall surface 1 d, and the mutual spacing between eachvertical guide structure 12, 12, . . . are adjusted. Subsequently, eachof the vertical guide structures 12, 12, . . . is secured to the upperguide structure 10 and the lower guide structure 11. By securing thesevertical guide structures 12, 12, . . . , the relative spacing in theleft and right directions (that is, the circumferential direction of thevertical guide structures 12, 12, . . . ) between the welding units 20,20, . . . attached to each of the vertical guide structures 12, 12, . .. , and the movement direction of each of the welding units 20, 20, . .. (that is, the direction of weld progression) can be set in a fixedmanner.

In this state, each of the welding units 20, 20, . . . is positioned atthe top end of its corresponding vertical guide structure 12, 12, . . .. Subsequently, power is supplied to each of the welding torches 85, 85on each of the welding units 20, 20, . . . , and with the shield gas(carbon dioxide gas) also being supplied, each of the welding units 20,20, . . . is moved concurrently downward at a predetermined speed, andoverlay welding is conducted by the welding torches 85, 85 (see thesolid line sections in FIG. 13). During this process, in this embodimentthere are provided eight welding units 20, each of which is equippedwith two welding torches 85, and consequently pairs of parallel weldbeads B₁, B₁ that are produced with a spacing that corresponds with thespacing between the pair of welding torches 85, 85, are formed in eightlocations around the inner wall surface 1 d with a predetermined spacingtherebetween, forming a total of 16 weld beads.

When the welding units 20, 20, . . . reach the bottom end of thevertical guide structures 12, 12, . . . , welding is temporarily halted,and the welding units 20, 20 . . . are raised, and placed in standbymode at the top end of the vertical guide structures 12, 12, . . . .

Next, the securing arrangement between the vertical guide structures 12,12, . . . and the upper guide structure 10 and the lower guide structure11 is released, each of the vertical guide structures 12, 12, . . . ismoved in the left or right direction by a predetermined distance (thatis, by a dimensional distance equivalent to the spacing of anaforementioned pair of welding torches 85, 85), and at this point thevertical guide structures 12, 12, . . . are once again secured to theupper guide structure 10 and the lower guide structure 11. In thisstate, each torch 85 of the welding units 20, 20 . . . is positionedbetween a pair of weld beads B₁, B₁, formed during the previous weldingrun.

In this state, each of the welding units 20, 20 . . . is reset to awelding capable state, and each of the welding units 20, 20, . . . isthen moved downward at a predetermined speed, and a second overlaywelding run is conducted by the welding torches 85, 85 (see the chainline sections in FIG. 13).

By repeating this welding operation a predetermined number of times, apredetermined region at a specific height on the inner wall surface 1 dof the digester 1 would be overlaid around the entire innercircumference, enabling an increase in the thickness of the inner wall 1c.

Next, the level is adjusted to the next level requiring overlay welding.In other words, first, the securing arrangement of the upper guidestructure 10 and the lower guide structure 11 relative to the inner wallsurface 1 d of the digester 1 is released, placing the guide structuresin a free state. Subsequently, each of the chain blocks 18, 18, . . . isoperated, and the suspended beam structure 9 is either raised or loweredby a predetermined distance (specifically, the distance in the heightdirection of the previous weld region). As the suspended beam structure9 is moved, the upper guide structure 10, the lower guide structure 11,and the vertical guide structures 12, 12, . . . (namely, theaforementioned guide mechanism Z) are raised or lowered in concert, andthe welding units 20, 20 . . . are positioned at the initial height forthe next overlay welding operation. Subsequently, by executing the samesequence as the previous welding run, the next overlay welding operationis conducted either above or below the previous overlay welded region.

By conducting sequential overlay welding operations while repeating thetype of left or right positional alteration of the welding units 20, 20. . . , and the positional adjustment in the height direction of theguide mechanism Z described above, the required thickness repairoperations is performed for all the sections of reduced thickness on theinner wall surface 1 d. Following completion of thickness repairoperations using overlay welding, the entire operation is completed bydisassembling and carrying out each of the components, in the reverseorder to that used during assembly.

Moreover, each of the exhaust systems 32 to 34 described above isoperated continuously through the entire period from the commencement ofpreparatory operations through to the completion of welding operations,and this ensures good ventilation within the digester 1, and guaranteesa safe operation performed in a good operating environment.

As described above, according to an overlay welding operations apparatusof this embodiment, the level adjustment accompanying the change of thewelding position in the height direction is achieved solely by asuitable movement of the suspended beam structure 9 in either an up ordown direction using the chain blocks 18, 18, . . . , and consequentlycompared with a conventional case in which a steel scaffold is put upinside the digester 1, and an operation for extending this scaffold mustbe conducted every time the welding height is altered, the operation foradjusting levels is markedly easier, the safety and operability of alloperations throughout the entire welding operation, including the leveladjustment operations, are improved, meaning the downtime for thedigester 1 during the thickness repair operations is shortened.

In addition, in the embodiment described above, the welding units 20 areattached to the suspended beam structure 9 via the guide mechanism Z andare able to be moved up and down as well as left and right, andconsequently the control of the operational status of the overlaywelding conducted by the welding units 20, namely, control of factorssuch as the width of the weld bead, the weld direction, or the spacingbetween adjacent weld beads, is far simpler and more reliable than acase in which the above factors are entrusted entirely to the actionsand judgment of an operator. As a result, overlay welding with asuniform a cladding as possible is formed over the entire regionrequiring overlay welding with a high level of reliability, resulting inan efficient extension of the life of the digester 1 by repairing thethickness of the wall.

Furthermore in this embodiment, the aforementioned posts 16, 16 are putup in a vertical direction inside the digester 1, the height adjustableoperations platform 14 is attached to each of these posts 16, 16 and ismovable in up and down direction under its own power, and consequentlyby using this height adjustable operations platform 14, operatingmaterials and operators are moved safely and rapidly to the position ofthe welding units 20, without requiring any scaffold height adjustments,even if the digester 1 is a blast furnace type structure of considerableheight, meaning both operational speed and safety are achieved.

In addition, in this embodiment, because the fixed operations platform13 is attached to the posts 16 in a manner that enables the attachmentheight to be altered, during the welding operations an operator easilyand accurately performs quality control checks of the welding producedby the welding units 20 from the fixed operations platform 13, meaningthe reliability of the overlay welding is further improved.

D: Other Factors

In the embodiment described above, the digester 1 was described as oneexample of the “tower structure” that is the target of the presentinvention, but the “tower structure” is not restricted to structuressuch as the digester 1 with a blast furnace type construction, and forexample, also includes comparatively low structures such as oil storagetanks and the like. In such cases, the posts 16 and the heightadjustable operations platform 14 may not necessarily be required.

Furthermore, the aforementioned “tower structure” is not restricted topressure vessels such as the aforementioned digester 1, and alsoincludes structures used at comparatively low pressures.

In addition, in the above embodiment, the description focused on weldingoperations on the inner wall surface of the digester 1 as arepresentative example, but the operations apparatus for an inner wallsurface and the operational method according to the present inventionare not restricted to this example, and can also be ideally applied to avariety of other operations including inspection operations,modification operations, and cleaning operations. Furthermore, each ofthese different types of operations may be conducted individually, or aplurality of operations may be conducted conjointly, in parallel. Inthose cases in which inspection operations, modification operations, orcleaning operations are conducted, the aforementioned welding units 20will be replaced, and an appropriate inspection device, modificationoperation device or cleaning device may be mounted to the guidemechanism Z.

Industrial Applicability

As described above, according to the present invention, by moving asuspended beam structure suspended below a suspension support base in anupward or downward direction, the height position within theaforementioned tower structure of an operations unit attached to thesuspended beam structure, in other words, the height setting within thetower structure of the operational target region for the operationsunit, is easily altered, and consequently compared with a conventionalcase where a scaffold is put up inside the tower structure, the heightof the scaffold need not be changed every time the operating height isaltered, and the operation for adjusting levels during operations ismarkedly easier, or even unnecessary, making the structure ideal forimproving the safety and operability associated with all manner ofoperations.

1-6. (canceled)
 7. An operations apparatus for an inner wall surface ofa tower structure, wherein a suspension support base is installed insidea tower structure, a suspended beam structure is suspended from saidsuspension support base in a manner that enables up and down movement,an operations unit is attached to said suspended beam structure via aguide mechanism in a manner that enables up and down and/or left andright movement, and operations are performed on an inner wall surface ofsaid tower structure using said operations unit, and said guidemechanism comprises an upper guide structure and a lower guide structurethat are separated and oppose each other across a vertical direction,and a vertical guide structure, which extends between each of said guidestructures and is disposed in a vertical direction, movable in a leftand right direction along said guide structures, and supports saidoperations unit in a manner that enables up and down movement.
 8. Theoperations apparatus for an inner wall surface of a tower structureaccording to claim 7, wherein said operations unit is equipped with atleast welding, inspection, modification, and cleaning functions.
 9. Anoperations apparatus for an inner wall surface of a tower structure,wherein a suspension support base is installed inside a tower structure,a suspended beam structure is suspended from said suspension supportbase in a manner that enables up and down movement, an operations unitis attached to said suspended beam structure via a guide mechanism in amanner that enables up and down and/or left and right movement, andoperations are performed on an inner wall surface of said towerstructure using said operations unit, and a post is put up in a verticaldirection inside said tower structure; and a height adjustableoperations platform being movable under its own power in the verticaldirection along said post and a fixed operations platform beingalterable its fixed vertical position relative to said post areinstalled.